Fresh Air Bypass to Cool Down Hot Exhaust in DPF Regeneration Mode at Low Vehicle Speed and Idle

ABSTRACT

An engine system includes a diesel engine having an exhaust manifold connected to the diesel engine. An exhaust passage is connected to the exhaust manifold and a diesel particulate filter is disposed in the exhaust passage. An air intake passage is provided for supplying fresh air to the diesel engine. A bypass passage is connected between the air intake passage and the exhaust passage in a location downstream of the diesel particulate filter. The bypass passage includes a bypass control valve for opening and closing the bypass passage during a diesel particulate filter regeneration cycle when the vehicle is at low speed or idle.

FIELD

The present disclosure relates to a diesel engine system, and moreparticularly to a diesel engine system incorporating a fresh air bypassto cool down hot exhaust in a diesel particulate filter regenerationmode at low vehicle speed and idle.

BACKGROUND AND SUMMARY

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

A diesel particulate filter is generally required for diesel engines tomeet particulate matter emission targets set by the EnvironmentalProtection Agency for 2007 model year and beyond. The diesel particulatefilter traps the particulate matter during normal operating conditionsand has to be regenerated periodically at high exhaust temperatures atany operating conditions. Generally speaking, the diesel particulatefilter regeneration interval is about 250 to 350 miles, depending on theduty cycles selected for the engine system. However, high exhausttemperatures of between 450 degrees Celsius and 600 degrees Celsius areencountered at the tailpipe exit during diesel particulate filterregeneration at idle, which raises a safety concern. To address theconcern, an exhaust cooler or jet pump has previously been located onthe tailpipe. The cooler entrains the surrounding air into the hotexhaust and lowers the exhaust temperature. In order to entrain asufficient amount of air, the nozzle diameter of the cooler usually issmaller than the diameter of the exhaust pipe. This restricts theexhaust flow and adds additional back pressure to the exhaust system.This consequently results in increased fuel consumption and limits themaximum power that can be developed at a rated condition. Any devicethat is added to the tailpipe for the purposes of cooling exhaust atidle could potentially increase the back pressure at rated condition.

The system of the present disclosure provides a bypass for passing freshair from the charger cooler outlet or inlet to the hot exhaust after thediesel particulate filter during a diesel particulate filterregeneration mode at idle and at low speed mode without adding backpressure. The fresh air will be mixed with the hot exhaust in thetailpipe and bring the exhaust temperature down at the exit.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawing described herein is for illustration purposes only and isnot intended to limit the scope of the present disclosure in any way.

The FIGURE provides a schematic diagram of the engine system accordingto the principles of the present disclosure incorporating a fresh airbypass to cool down the hot exhaust in the diesel particulate filterregeneration mode at low vehicle speed and idle.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

With reference to the FIGURE, the engine system 10 of the presentdisclosure will now be described. The engine system 10 includes a dieselengine 12 including an engine block having a plurality of bores definingcylinders 14. An air intake manifold 16 is connected to the engine forproviding intake air to the cylinders 14. An air intake passage 18 isconnected to the air intake manifold 16 and includes an intake throttlevalve 20 in communication with a turbocharger 21 and a charger aircooler 24 for providing compressed cooled air to the engine 12.Turbocharger 21 includes a compressor 22 in communication with intakeair and a variable geometry (VG) turbine 32 in communication with theexhaust gas.

An air exhaust manifold 28 is provided in communication with thecylinders 14 of the engine 12 and is connected to an exhaust passage 30.The VG turbine 32 is in communication with the exhaust passage 30 anddrives the compressor 22. Turbochargers with a variable geometry turbinechange the output of the turbine as a function of engine load. In thisway the optimum boost pressure can be maintained and optimum use can bemade of the energy in the exhaust gas. Cross-sectional changes are madeby resetting the turbine blades (smaller contact surface at low speeds,larger contact surface at high speeds). VG turbine turbochargers areparticularly efficient at partial load and eliminate “turbo lag”. Theyincrease engine power, increase throttle response and can also have abeneficial effect on particulate emissions. In addition, they open newperspectives regarding the control of exhaust gas recirculation. The hotexhaust from the engine cylinder spins the turbine which drives thecompressor to boost the intake pressure.

An exhaust gas recirculation passage 34 is provided with an exhaust gasrecirculation valve 36 that communicates exhaust gasses from the exhaustpassage 30 back to the intake passage 18 as controlled by an enginecontroller 50. The exhaust passage 30 further includes a dieseloxidation catalyst (DOC) and NO_(x) device 40 and a diesel particulatefilter 42 for filtering particulate matter from the emissions. Thediesel oxidation catalyst converts the emissions to oxide HC, CO and NOfrom the engine and provides heat and necessary chemical species todownstream catalyst converters. The NOx device reduces engine-out NO_(x)emissions. A diesel after-treatment system, which is composed of DOC,NO_(x) devices and a Diesel Particulate Filter (DPF), will control theharmful engine emissions like hydrocarbon (HC), nitrogen oxide (NO_(x)),particulate matter (PM), carbon monoxide (CO) and so on.

The engine system 10 further includes a bypass passage 44 that cancommunicate from the outlet side of the charger cooler 24 to thedownstream side of the diesel particulate filter 42. A bypass passage 45can alternatively be connected to the upstream side of the chargercooler, as illustrated in dashed lines, and connected to the exhaustpassage 30 at the downstream side of the diesel particulate filter 42. Abypass valve 48 is provided in the bypass passage 44 and is incommunication with an engine controller 50 that controls the enginesystem 10 to operate in a diesel particulate filter regeneration modebased upon a selected duty cycle. The diesel particulate filter 42 willcapture particulate matter entrained in the diesel exhaust on a ceramicor metallic substrate. At a certain point this particulate matter may beremoved through regeneration, the process by which the temperature ofthe exhaust flowing through the DPF reaches a sufficient level to simplyburn away the built-up particulates. In many cases, especially wherethere is a great amount of engine cycling or vehicle stopping andstarting, temperatures may not remain high enough for a sufficient timeperiod to remove the particulate matter. In those cases, active systemsare required, most of which involve burning a small amount of dieselfuel in the exhaust stream to raise the temperature enough to burn awaythe particulate matter. An active DPF regeneration typically takes about20-30 min. When the engine system 10 is in the diesel particulate filterregeneration mode, and the engine 12 is either at idle or at low speed(5 mph or less), the engine controller 50 controls the bypass valve 48to allow fresh air from the intake passage 18 to be bypassed to theexhaust tailpipe 52 where the fresh air is mixed with the hot exhaustgases to provide a reduced exhaust temperature at the exit of thetailpipe 52. The turbocharger 21 provides compressed air at a pressuregreater than the pressure of the pressure of the exhaust gas.

With the system of the present disclosure, there is no increase of backpressure that results in lower fuel economy. Furthermore, there are nomoving parts in the exhaust system and there is no impact on engineperformance during other driving conditions. The system also adds verylittle cost, including only the additional bypass passage tubing andbypass valve. The high pumping loss due to fresh charge air bypassenhances the capability of the diesel particulate filter regenerationcycle when the vehicle is at idle.

1. An engine system, comprising: a diesel engine; an exhaust passage in communication with an exhaust gas from the diesel engine; a diesel particulate filter disposed in the exhaust passage; an air intake passage for supplying air to the diesel engine; and a bypass passage connected between the air intake passage and the exhaust passage at a location downstream of the diesel particulate filter, the bypass passage including a bypass control valve for opening and closing the bypass passage.
 2. The engine system of claim 1, further comprising a turbocharger that provides compressed air to the air intake passage.
 3. The engine system according to claim 2, wherein the turbocharger provides the compressed air to a charger cooler, the bypass passage being connected to the air intake passage downstream of the charger cooler.
 4. The engine system according to claim 2, wherein the turbocharger provides the compressed air to a charger cooler, the bypass passage being connected to the air intake passage downstream of the turbocharger and upstream of the charger cooler.
 5. The engine system of claim 2, wherein the compressed air is provided to the bypass passage, the compressed air being at a pressure that is greater than a pressure of exhaust gas in the exhaust gas passage at the location downstream of the diesel particulate filter.
 6. The engine system according to claim 1, wherein the air intake passage includes an intake throttle valve downstream of the bypass passage.
 7. The engine system according to claim 1, further comprising an engine controller for periodically operating the engine system in a diesel particulate filter regeneration mode and for opening the bypass control valve during the diesel particulate filter regeneration mode.
 8. The engine system according to claim 1, further comprising an engine controller for periodically operating the engine system in a diesel particulate filter regeneration mode and for opening the bypass valve when the engine is in the diesel particulate filter regeneration mode and the engine is at idle.
 9. The engine system according to claim 1, further comprising an engine controller for periodically operating the engine system in a diesel particulate filter regeneration mode and for causing the bypass valve to open when the engine is in the diesel particulate filter regeneration mode and the engine is driving a vehicle at a speed of 5 miles per hour or less.
 10. An exhaust treatment system for an engine, comprising: an exhaust passage adapted to be connected to the engine; a diesel particulate filter disposed in the exhaust passage; an air intake passage adapted for supplying air to the engine; a bypass passage connected between the air intake passage and the exhaust passage at a location downstream of the diesel particulate filter, the bypass passage including a bypass control valve for opening and closing the bypass passage.
 11. The exhaust treatment system according to claim 10, further comprising a turbocharger that provides compressed air to the air intake passage
 12. The exhaust treatment system according to claim 11, wherein said turbocharger provides the compressed air to a charger cooler, the bypass passage being connected to the air intake passage downstream of the charger cooler.
 13. The exhaust treatment system according to claim 11, wherein the turbocharger provides the compressed air to a charger cooler, the bypass passage being connected to the air intake passage downstream of the turbocharger and upstream of the charger cooler.
 14. The exhaust treatment system according to claim 11, wherein the compressed air is provided to the bypass passage, the compressed air being at a pressure that is greater than a pressure of exhaust gas in the exhaust gas passage at the location downstream of the diesel particulate filter.
 15. The exhaust treatment system according to claim 10, wherein the air intake passage includes an intake throttle valve downstream of the bypass passage.
 16. A method comprising: regenerating a diesel particulate filter that is in communication with an exhaust gas from a diesel engine; and providing communication between an intake air source and the exhaust gas at a location downstream of the diesel particulate filter during the regenerating.
 17. The method of claim 16, further comprising compressing air supplied to the intake air source and providing the compressed air to the location downstream of the diesel particulate filter. 